In order to obtain information about the heights and times of future tides, tide tables, such as those produced by the National Oceanic and Atmospheric Administration must be consulted. These tide tables are constructed to provide tide information at various locations along given coastlines. In general, to obtain tide information at one of the specific locations for which tide information is available, two different tables must be consulted. A table of baseline tide information is first consulted. This table of baseline information provides the tide time and tide height on different dates for a single baseline location along the coastline for which the particular table is constructed.
If the location for which tide information is desired is the baseline location (for which tide information is provided), then the tide information is taken directly from the table of baseline information and the second table does not need to be consulted. Most often, however, tide information is desired for locations other than the baseline location. To avoid having to compile complete tide tables for every location along a given coastline, the National Oceanic and Atmospheric Administration has compiled a complete tide table only for a baseline location, along each major coastline, and then provides offsets for other locations along that coastline. These offsets include a time offset, a high tide height offset, and a range. The time offset is the difference in hours and minutes between when a tide occurs at the baseline location and when the same tide occurs at the location for which the offset applies. A positive time offset indicates that the tide occurs at the offset location later than at the baseline location. A negative time offset indicates that the tide occurs at the offset location earlier than at the baseline location. The high tide height offset is the difference in feet between the height of a high tide at the baseline location and the height of a high tide at the location for which the offset applies. The range is the difference between the height of the high tide and the height of the low tide, at the offset location. Therefore, given the height of the high tide at the baseline location, the high tide offset, and the range, then the height of both the high and low tides can be calculated for the offset location.
Therefore, after the baseline information is found in the first table, then offsets are found in a second table. These offsets are applied to the baseline tide information to get the correct tide information for the required location.
For example, a 1988 tide table which purports to be "for the coast of Southern California" provides the following baseline values for Monday, Nov. 21, 1988:
______________________________________ HIGH TIDE LOW TIDE AM Ht. PM Ht. AM Ht. PM Ht. ______________________________________ 6:57 7.1 8:55 4.6 12:35 1.1 1:52 -1.0 ______________________________________
Where AM and PM are the respective times of day and Ht. is the height of the tide in feet. Note that each tide, high and low, occurs twice each day. This tidal information is only accurate for a single specific geographic location somewhere along the coast of Southern California, such as Los Angeles. If the user of the table is interested in obtaining precise tidal data for a different specific location, such as Muertos Bay, Calif. then the following offsets must be applied to the above-shown tidal times and heights:
______________________________________ Time Height of Range of Tide High Tide of Tide (h/m) (feet) (feet) ______________________________________ Lower California -0:45 0.65 2.8 Muertos Bay ______________________________________
where h/m is the time in hours and minutes and the height of the low tide is equal to the height of the high tide minus the range. Similarly, if the user of the table is interested in a more northerly location, such as San Clemente, Calif., the following different offsets would be applied to the tabular data:
______________________________________ Time Height of Range of Tide High Tide of Tide (h/m) (feet) (feet) ______________________________________ California -0:18 0.91 3.7 San Clemente ______________________________________
Accordingly, in order to obtain accurate tidal data for specific coastal locations, a certain amount of mathematical manipulation of the available tabular data is required. Moreover, in order to make use of the tide tables, one must keep a tide table book on his person or at some readily accessible place so as not to be without the necessary information when it is needed.
Tide information is important to marine navigators, boaters, fishermen, and coastal dwellers. Many activities, particularly those of commercial vessels, require planning weeks or more in advance. Deep draft ships, for instance, may only use certain waterways during high tide. Therefore, it is necessary for these navigators to consult tide tables such as those produced by the National Oceanic and Atmospheric Administration. Frequently, persons planning recreational events have no access to tide information and rely solely upon chance in scheduling. However, if the fishing, for example, is always better in a certain area at high tide, then it makes sense to plan the fishing trip in advance so that the fishing will take place when the tide is high.
An explanation of the many factors affecting tide heights and times is important to this invention because the prior art neglects to take into consideration all of these factors in determining tide times, whereas the present invention does consider all of these factors.
Tides are caused primarily by the gravitational forces of the sun and the moon acting upon the earth's oceans. Because the moon is closer to the earth than the sun, its influence is approximately twice as great as the sun's. The combined gravitational forces of the sun and the moon cause the oceans of the earth to bulge on diametrically opposite sides of the earth. The height of the water in this bulge is greater than in the surrounding non-bulging areas, therefore we have tides. The actions of the sun and moon result in tides having a duration of twelve hours and twenty-five minutes between highs. Because a flood tide is approximately five hours in duration and an ebb tide is approximately seven hours in duration, this results in a time of approximately six hours and thirteen minutes between a high tide and its next low tide.
In addition to the effects of the sun and moon, tides are also affected by seasonal changes, climate, and geography. Seasonal changes cause variations in the tides because the distance between the sun and the earth changes during the year. Climate affects tides on a daily basis as barometric pressure and winds affect the flow of water upon the earth's surface. Geography is a major consideration because the tidal bulge varies from place to place upon the earth's surface. Therefore, the amount of tide experienced at any given moment depends upon the exact location considered.
All of the prior art devices operate strictly by calculating the time of the next high or low tide based upon the relation of tide times to chronological time.
Tides in their diurnal cycle, occur each time slightly later in the day. The delay is approximately 25 minutes for each individual cycle. That is about 50 minutes for a complete diurnal cycle in a 24-hour period.
For example, if a high tide occurred at 12:00 noon on Saturday, then the next high tide would be at 12:25 midnight and the following high tide would occur at 12:50 Sunday afternoon.
As is evident from the above discussion, tide occurs on a regular basis and on a schedule where the time between tides is a constant ratio to chronological time. This ratio, which is determined by celestial factors, is 57/59. It is this ratio that prior art devices use to calculate the time of the next high or low tide. Other factors, such as seasonal changes, climate, and geography are not considered at all by prior art devices.
Mechanical watches are well known which indicate both the present time and the time of the next high or low tide. U.S. Pat. No. 4,035,617, issued to Banner, discloses a typical prior art mechanical watch wherein the clock face has a high tide and a low tide indication. The high tide indication is at the 12 o'clock position and the low tide indication is at the 6 o'clock position on the watch face. A third hand, which is operated by the clock movement, indicates whether the next tide is to be high or low by pointing to the appropriate tide indication on the watch face.
U.S. Pat. No. 4,412,749 issued to Showalter, discloses an electronic clock which alternately displays the present time and the time of the next high or low tide. Whether the next tide will be high or low is indicated by a colored light.
Neither prior art mechanical watches nor the prior art electronic clock provides a convenient indication of tide times in the future. The prior art devices only indicate the time of the next high or low tide. While knowing the time of the next high or low tide is certainly useful, it does not help in planning beyond a few hours into the future.
Neither prior art mechanical watches nor the prior art electronic clock provides any indication of tide height. Knowledge of future tide height can be crucial to some users. For instances, a deep draft ship may require a minimal tide height in certain waterways.
Although the prior art has recognized to a limited extent the need to have tide information readily accessible, the proposed solutions have to date been ineffective in providing a satisfactory remedy. Therefore, there exists a substantial need in the art for an improved tide-indicating device.